Which of the Following Is Always True for All Probability

Short Answer

Which of the following is always true for all probability density functions of continuous random variables? $\begin{array}{|l|l|}\hline A&\text {They are symmetrical. }\\\hline B&\text { They are bell-shaped.}\\\hline C&\text {The area under the curve is 1.0 . }\\\hline D&\text {They have the same height. }\\\hline \end{array}$